Ionograms are an image of frequency versus time delay (virtual height) of HF echoes from the ionosphere recorded by an ionosonde.
An ionosonde is a swept frequency HF pulsed radar used to monitor the ionosphere. SWS WDC has archived ionogram data from
30 stations, 12 of them are still active at present. An CADI (Canadian Advanced Digital Ionosonde) ionosonde has been sounding
since 30/11/1999 at Casey. The CADI vertical sounding ionosondes normally sweep in frequency from about 1 to 20 MHz. Three
standard sweeps are provided: low resolution (100 frequencies), medium resolution (200 frequencies), high resolution (400
frequencies). The step size may be selected to be linear or logarithmic. The step interval is variable, becoming more coarse
at higher frequencies as ionograms are generally displayed on a logarithmic scale. Height range up to 512 km (to be increased
to 1000 km) with 6 km resolution. Every five minutes, a Ionogram data file is recorded, cleaned and the cleaned ionogram is
transfered to SWS Sydney head office for autoscaling and further analysis. The raw ionogram file is recorded in a DVD monthly,
which will be posted to Sydney SWS head office every month. During 07/02/1993 to 08/10/2001, Casey also had an Lowell ionosonde.
SWS WDC archives all raw ionogram files and cleaned ionogram files. The Casey digital clean ionogram data is available since
25/11/1997, and digital raw ionogram data since 07/02/1993. The Casey scaled hourly ionospheric data include parameters of
foF2, foF1, FoE, foEs, fbEs, fmin, fxl, f'scaling F/s, M(3000)F2, h'F2, h'F, h'E, h'Es, h'Scaling R/S and Type Es. They are
avalable since 01/01/1957. The Casey median data of foF2 and M(3000)F2 are available since 07/1957.

Parameter #2

Name

Virtual Height

Description

The apparent height of an ionospheric layer deduced from the time delay of a reflected radio pulse upon the assumption that
it travelled at the speed of light over its entire path. However, the radio wave actually slows down as it is refracted so
that the virtual height is greater than the true height of the refracting layer.